Study: Edges of magnetic tape key to boosting data density

April 16, 2003

COLUMBUS, Ohio -- Ohio State University engineers have examined in unprecedented detail a key manufacturing step that could improve one of the worlds most popular data storage materials: magnetic tape.

Bharat Bhushan

How a tape is cut in the factory plays a major role in how much data it can hold -- and whether the $6 billion American magnetic tape industry will be able to maintain its market share in the future, according to the comprehensive study.

Businesses ranging from storefronts to major corporations often back up essential computer records on tape, explained Bharat Bhushan, Ohio Eminent Scholar and the Howard D. Winbigler Professor of mechanical engineering at Ohio State. Consumers use the same kind of tape in audio and video cassettes.

As the worlds information needs grow, tape manufacturers are trying to boost storage capacity, said Bhushan. To compete with the industrys top rival -- computer hard disks -- multi-track tapes will have to carry even more tracks. At the same time, tape width will have to shrink so that cartridges can be smaller.


The tape edge measures only a fraction of the width of a human hair, but the image they saw might as well have been a satellite photo of the Grand Canyon.


Thats the number one challenge, according to our industry partners, Bhushan said. When you put more tracks on a narrower tape, you use more of the surface. The quality of the tape edge becomes more important than ever before.

During their nine-month study, Bhushan and graduate student Anton Goldade literally put magnetic tape under the microscope. The tape edge measures only a fraction of the width of a human hair, but the image they saw might as well have been a satellite photo of the Grand Canyon.

If you look at a brand new strip of tape with the naked eye, it looks perfectly smooth, but when you look closer, you see all these imperfections, said Goldade.

Torn ridges and grooves ran all along the edge -- signs of stress from when the tape was cut during manufacturing.

In the factory, rotating blades cut large sheets of plastic into strips that form the backbone of the tape. Matched sets of blades cut the tape from both sides, like a pair of scissors. As the blades become dull, they cut less cleanly, and the tape rips along the edges, the engineers found. They published their study in the April 2003 issue of the journal Tribology Letters.

Normally these microscopic tears wouldnt matter; they wouldnt cause a tape to break during normal use. But over time, they could grow large enough to damage the coating of magnetic material near the tape edges, destroying any data stored there, Bhushan said. Whats more, tapes with more tracks would have to wind and unwind many more times in a tape machine, which could make the tears grow even larger.

He and Goldade developed a technique to gauge the quality of a tape edge, as well as techniques to measure the forces that affect tape condition over time.

The engineers said their techniques could be used for quality control in the factory. For instance, manufacturers could examine samples of freshly cut tape to better judge when to sharpen or replace cutting blades, Goldade said.

The largest American tape maker, Imation Corp. of Oakdale, MN, supplied tapes for the project, while funding came from a U.S. Department of Commerce Advanced Technology Program to promote the U.S. data storage industry.

Because the storage capacity of hard disks has increased dramatically in the last decade, some industry analysts have suggested that disks will one day push magnetic tape from the market.

People think the tape drive is dead, but thats far from the truth, said Bhushan. He cites IBM Corp.s recent sale of its hard drive business to Japans Hitachi Ltd. as evidence that hard drives are experiencing the same economic troubles as other data storage technologies.

Currently, some magnetic tape cartridges measure 3.5 inches (9 centimeters) on a side and can hold 200 gigabytes of information -- the equivalent of 800 sets of encyclopedias.

You can carry it in your pocket, said Goldade.

He pointed out that tapes are also safe from Internet attacks and hardware failures because they arent attached to a computer when theyre in storage.

Along with this study of tape edge quality, Bhushans laboratory is pursuing related projects, including a new mechanism for guiding tape through a tape machine. The industrial partner on that project is Segway Systems LLC of Littleton, Colorado.

Were looking at the full spectrum of this problem --improving the tape edge plus the design of tape drives, Bhushan said.
Additional Contact:
Anton Goldade, (614) 292-2289;

Written by Pam Frost Gorder, (614) 292-9475;

Ohio State University

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